Rotation speed detection device having a rotation angle detector of inductive type

ABSTRACT

A detection head unit comprises a stator and a rotor. The stator has four poles disposed circumferentially at an interval of 90°. The poles have primary coils and secondary coils wound thereon. Two radially opposing poles constitute a pole pair. The primary coils wound on the poles constituting the pole pair are connected in series and in opposite phase with each other and one pole pair is excited by a sine wave signal and the other pole pair by a cosine wave signal. The rotor is of such a configuration, e.g. an eccentric rotor, as to change reluctance of the respective stator poles in accordance with a rotation angle and change reluctance in a differential manner between the two poles constituting the pole pair. An output signal resulting by phase shifting the sine wave signal applied to the primary coil in accordance with a rotation angle of the rotor is provided by a secondary coil. The rotation angle is detected by measuring phase difference between the reference signal and the output signal of the secondary coil. The rotation speed can be detected by detecting difference in frequency or period between the reference signal and the output signal. Further, acceleration in rotation can be detected by detecting an amount of change in the rotation speed. The detection device of a high resolution can be obtained by providing teeth of a certain pitch on the periphery of the rotor and teeth corresponding to the rotor teeth on the stator poles.

BACKGROUND OF THE INVENTION

This invention relates to a variable reluctance type rotation angledetection device capable of detecting not only rotation angle but also arotation speed and rotation acceleration together by using a commondetection head unit and, more particularly, to a detection devicecomprising a variable reluctance type detection head unit producing anoutput signal by phase shifting or phase modulating a reference ACsignal in accordance with a present position of rotation.

Known in the art of rotation angle detectors are a potentiometer, aresolver, a rotary differential transformer, an optical rotary encoderand the like device. A potentiometer is short in life for it is acontact type device. A resolver which needs a brush has problems indurability, high speed response and noise. Although there exists aresolver which has obviated a brush by providing a rotary transformer,provision of such rotary transformer has the disadvantage that thedevice requires a complicated and large device. A rotary differentialtransformer which obtains an analog output corresponding to a sine waveamplitude corresponding to a rotation angle is incapable of producing alinear output over all of the rotation range. A common disadvantage inthe rotary differential transformer and the potentiometer is that thesedevices tend to cause errors due to disturbance, for they produce avoltage level corresponding to a rotation angle. For example, in thesedevices, variation in resistance of a coil due to change in thetemperature causes variation in the level of the detection signal.Reliability in these devices is inadequate because attenuation of thelevel in signal transmission paths from the detector to a circuitutilizing the detection signal differs depending upon the distance ofthe transmission paths. Further, variation in the level due to noise isdirectly outputted as a detection error. For the various reasons statedabove, it is difficult to construct an absolute encoder of a highresolution by the prior art electromagnetic type rotation angledetector. On the other hand, the optical type encoder which has afunction of an absolute encoder is disadvantageous in that itsresolution of detection is limited by an area of a pattern disk so thatan increase in resolution necessitates an increase in the area of thepattern disk with a result that a large pattern disk and, accordingly, alarge detector is required. The optical type encoder is alsodisadvantageous in that it is generally expensive, that the wholepattern disk must be replaced if change in resolution or a code type ofdata is required and that the pattern disk tends to get broken if it ismade of a glass plate so that an environment in which it can be used islimited.

Prior art rotation speed meters are generally classified into thosewhich produce an analog voltage (or current) proportionate to therotation speed (i.e., revolution number per unit time) and those whichproduce a pulse train proportionate to the rotation speed. Commondisadvantages in the devices producing an analog output are that, asdescribed above, they tend to cause errors due to disturbance and thatincrease in resolution is limited. The devices producing a pulse trainare also limited in resolution and rangebility (range of detectablerevolution number), for the number of pulse produced per one rotation islimited due to the mechanism of the device. Besides, there has been norotation acceleration meter having a wide detection range and a highresolution.

THE SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide avariable reluctance type rotation angle detection device which is of anon-contact type, simple and compact in construction, capable ofperforming an accurate detection without being affected by variation inthe output level due to disturbance, durable in hard environments andpossessed of a high resolution.

It is another object of the invention to provide a detection devicewhich is of a high resolution and capable of detecting a rotation speedin a wide range.

It is another object of the invention to provide a detection devicewhich is of a high resolution and capable of detecting rotationacceleration in a wide range.

It is another object of the invention to provide a detection devicecapable of detecting not only a rotation angle but also rotation speedand rotation acceleration by a common detection head unit.

It is still another object of the invention to provide a detectiondevice capable of detecting the rotation angle, rotation speed androtation acceleration with a higher resolution. This object can beachieved by a rotation angle detection device including a stator havingpoles and primary and secondary coils wound on the poles and a rotor ofsuch a configuration that reluctance of a magnetic circuit for each poleis changed in accordance with a rotation angle output signal beingproduced by the secondary coils on the basis of reference AC signalswhich have been phase shifted in accordance with the rotation angle ofthe rotor by exciting the primary coils of the respective stator polesby the reference AC signals which are different in phase from oneanother. Data corresponding to the rotation angle can be obtained bydetecting phase difference between the reference AC signal and theoutput signal of the secondary coil. When the rotor is being rotated,the output signal of the secondary coil is a signal produced by phasemodulating the reference AC signal in accordance with the rotationspeed. Accordingly, data corresponding to the rotation speed can beobtained by detecting difference in the frequency or period between thereference AC signal and the output signal of the secondary coil.Besides, by obtaining data corresponding to the rotation speedmomentarily, change in the rotation speed, i.e., rotation acceleration,can be computed on the basis of difference between a newly obtainedvalue and a previous value of the rotation speed. Thus, the rotationangle, the rotation speed and the rotation acceleration can be detectedtogether by using a single rotation angle detection device.

Since no coil is wound on the rotor, the detection device according tothe invention is of a brushless type which is naturally durable.Besides, the detection device enjoys a simplified construction becauseno rotary transformer which was indispensable in the prior art brushlessdetection device is required. Since the detection device has employed asystem of obtaining an angle by detecting phase difference, an accuratedetecting of angle can be made regardless of variation in the outputlevel due to disturbance. Resolution of detection of the rotation anglecan be increased simply by making a circuit design for increasingresolution of detecting the phase difference such as increasing the rateof a clock pulse used in a counter for counting phase difference.Accordingly, no large device such as the prior art optical type rotaryencoder is required. The detection device according to the invention,which has no fragile component part such as a glass pattern disk, isstrong in hard environments. Further, since no load is applied from theside of the detection device on a shaft in which detection is to bemade, there is scarcely limitation in the load on the shaft.Furthermore, absolute data of the rotation angle can be obtained underany temperature condition and in any environment by using, for detectionof phase difference, the same clock pulse as that used for establishingthe frequency of the reference AC signal.

The stator preferably comprises plural pairs of poles which are excitedin opposite phase to each other and the rotor is so configured thatdifferential reluctance change is produced between the two polesconstituting a pair. Increase in resolution of detection can be broughtabout by this arrangement.

Further increase in resolution of detection can be realized by providingteeth of a certain pitch about the rotor and providing correspondingteeth also about the stator poles. By determining relationship betweenthe rotor teeth and the stator teeth in such a manner that change inreluctance which completes one cycle for each pitch of the rotor teeth,a relative rotation angle within one pitch of the teeth can be detectedwith a high resolution.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1(a) is a side sectional view of an embodiment of the detectionhead in the rotation angle detection device according to the invention;

FIG. 1(b) is a front view of the embodiment shown in FIG. 1(a);

FIG. 2 is a circuit diagram of a circuit equivalent to a magneticcircuit in the detection head unit shown in FIGS. 1(a) and 1(b);

FIG. 3(a) is a side sectional view of another embodiment of thedetection head unit according to the invention;

FIG. 3(b) is a front view of the embodiments shown in FIG. 3(a);

FIG. 4(a) is a side sectional view of another embodiment of thedetection head unit according to the invention;

FIG. 4(b) is a front view of the embodiment shown in FIG. 4(a);

FIG. 5(a) is a side sectional view of still another embodiment of thedetection head unit according to the invention;

FIG. 5(b) is a front view of the embodiment shown in FIG. 5(a);

FIG. 6 is a block diagram showing an example of a reference AC signalgeneration circuit and a phase difference detection circuit in therotation angle detection device according to the invention;

FIG. 7 is a time chart showing the operation of the reference AC signalgeneration circuit in FIG. 6;

FIG. 8 is a time chart showing the operation of the phase angledetection circuit shown in FIG. 6;

FIG. 9 is a block diagram showing a modified example of the reference ACsignal generation circuit and the phase difference detection circuitshown in FIG. 6;

FIG. 10 is a block diagram showing an example of a phase differencedetection circuit which detects the phase difference in an analogquantity;

FIG. 11 is a time chart showing examples of output waveforms in someportions in the circuit of FIG. 10;

FIG. 12 is a block diagram showing another example of the phasedifference detection circuit detecting the phase difference in an analogamount;

FIG. 13 is a time chart showing examples of output waveforms of someportions in the circuit shown in FIG. 12;

FIG. 14(a) is a side sectional view of the detection head unit accordingto the invention;

FIG. 14(b) is a front view of the circuit shown in FIG. 14(a);

FIG. 15(a) is a side sectional view of still another embodiment of thedetection head unit according to the invention;

FIG. 15(b) is a front view of the embodiment shown in FIG. 15(a);

FIG. 16 is a diagram showing an example of frequency deviation of theoutput signals of the secondary coils in the embodiments of thedetection head unit depending upon the angular velocity or angularacceleration of the rotating shaft;

FIG. 17 is a block diagram showing an example of a circuit for detectingthe rotation speed and rotation acceleration in response to the outputsignal from the detecting head unit;

FIG. 18 is a time chart showing examples of output waveforms in someportions of the circuit of FIG. 17;

FIG. 19 is a block diagram showing another example of the circuit fordetecting the rotation speed and rotation acceleration;

FIGS. 20, 21 and 22 are block diagrams respectively showing an exampleof the frequency measurement circuit in FIG. 19;

FIG. 23 is a time chart showing examples of output waveforms in someportions of the circuit in FIG. 22;

FIG. 24(a) is a radical sectional view of an embodiment of a highresolution type detection head unit according to the invention;

FIG. 24(b) is an axial sectional view of the embodiment shown in FIG.24(a);

FIG. 25 is a view for illustrating relationship between teeth formed inthe rotor and teeth formed in the stators shown in FIGS. 24(a) and24(b);

FIG. 26 is a side elevation and block diagram showing schematically anexample of a combination of the high resolution type detection head unitand a detection head unit for detecting an absolute rotation angle foreach tooth provided on the same shaft;

FIG. 27 is a graphical diagram showing absolute angle detection data andhigh resolution relative angle detection data obtainable from the deviceshown in FIG. 26 with a vertical axis representing detected values and ahorizontal axis representing the angle;

FIG. 28 is an exploded prespective view of another embodiment of thehigh resolution type detection head unit according to the invention;

FIG. 29(a) is an axial sectional view showing another embodiment of thehigh resolution type detection head unit;

FIG. 29(b) is a sectional view of the detection head unit taken alongline b--b in FIG. 29(a);

FIG. 30(a) is a side view of another embodiment of the high resolutiontype detection head unit;

FIG. 30(b) is a front view of the detection head unit shown in FIG.30(a);

FIG. 31(a) is an axial sectional view of still another high resolutiontype detection head unit;

FIG. 31(b) is a sectional view of the detection head unit taken alongline b--b in FIG. 31(a); and

FIG. 32 is a diagram of an example of phase shift circuit for adjustingorigin between the secondary coil output terminal and phase differencedetection circuit.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1(a) and 1(b), a stator 1 has four inwardlyprojection poles A, B, C and D disposed with an interval of 90° relativeto each adjacent pole in a circumferential direction. The radiallyopposing poles A and C constitute a pole pair and the radially opposingpoles B and D constitute another pole pair. Primary coils 2A and 2C (2Band 2D) are wound on the pole pair A and C (B and D) in a differentialmanner. Assuming that the direction of flux toward the end of therespective poles is a positive phase, the respective coils are wound insuch a manner that fluxes produced by the windings 2A and 2C (or 2B and2D) are in opposite phase to each other. More specifically, the primarycoils 2A and 2C are wound in a differential manner so that, if a flux isproduced in the pole A by the primary coil 2A in a direction indicatedby an arrow X, i.e., in a direction coming from the root of the pole A,a flux is produced in the opposite pole C by the primary coil 2C in adirection indicated by an arrow X, i.e., in a direction entering theroot of the pole C. By this arrangement, a flow of flux of the samedirection is produced in the pole pair A and C through a rotor 3provided in a central space between the pole pair. Likewise, the primarycoils 2B and 2C are wound on the other pole pair B and D. The reason forwinding the primary coils in a differential manner is that, as will bedescribed later, the pole pair A and C is excited by an AC signaldifferent from an AC singal used for exciting the pole pair B and D sothat a common flow of flux should be guaranteed in the poles (A" and C"or B" and D") which are excited by the common AC signal. The rotor 3consists of a core only and no coils are wound thereon. The cores of thestator 1 and the rotor 3 are of course made of materials of a relativelyhigh permeability.

The rotor 3 opposing the respective ends of the poles A-D with asuitable gap is rotated integrally with a rotating shaft 4. A rotationangle θ to be detected is given to the shaft 4. The rotor 3 has such aconfiguration that reluctance of magnetic paths passing the poles A, B,C and D is changed in accordance with the rotation angle θ. In theembodiment shown in FIG. 1, the rotor 3 is of a cylindricalconfiguration and is mounted on the shaft 4 eccentrically to the axis ofthe shaft 4. Owing to this eccentric cylindrical configuration, thelength of the gap between the peripheral surface of the rotor 3 and eachof the poles A, B, C and D changes in accordance with change in therotation angle θ. In response to the change in this gap, change inreluctance corresponding to trigonometric function for one cycle isproduced in the respective poles A, B, C and D of each rotation of therotor 3.

The pole pair consisting of the poles A and C and the pole pairconsisting of the poles B and D are excited separately and individuallyby AC signals which are out of phase by 90°. In the embodiment shown inFIG. 1, the primary coils 2A and 2C on the poles A and C are connectedin series and a sine wave signal ia=I sin ωt is applied to these coilsfrom an oscillator 5. The primary coils 2B and 2D on the poles B and Dare connected in series and a cosine wave signal i_(b) =I cos ωt isapplied to these coils from an oscillator 6. It should be noted thatwhile the primary coils 2A and 2C appear as if they were connected inseries and in phase with each other if the direction of winding only isobserved, they are actually connected in series but in opposite phase toeach other due to the directions of the poles A and C on which thesecoils are wound, i.e., directions of the fluxes produced in these poles(in other words, these coils are wound in a differential manner). Thesame is the case with the primary coils 2B and 2D.

A secondary coil 7 is provided to the stator 1 to collect the voltageinduced by the poles A, B, C, and D. In the embodiment shown in FIG. 1,secondary coils 7A and 7C are wound around the poles A and C in phasewith each other but in opposite phase to other secondary coils 7B and 7Dwhich are wound around the poles B and D in phase to each other. Thesesecondary coils 7A to 7D are connected in series to output the signal Ewhich is the total of the voltages induced by the poles A, B, C, and D.The signal E is shifted in phase by the phase angle corresponding to therotation angle θ of the rotor 3 with respect to the phase of theexciting reference AC signal i_(a) =I sin ωt or i_(b) =I cos ωt. Whilereadily confirmable by a test device, this may be provided as follows.

An equivalent circuit of the magnetic circuit formed in the detectionhead unit in FIG. 1 is schematically shown in FIG. 2 wherein N indicatesthe number of turns of the primary coils 2A, 2B, 2C and 2D while i_(a)and i_(b) indicate the instantaneous current values of the exciting ACsignals I sin ωt and I cos ωt so that Nia, Nib, -Nia, and -Nib indicatethe magnetomotive forces generated by the primary coils 2A to 2D of thepoles A to D, respectively. P_(A), P_(B), P_(C), and P_(D) indicatepermeances generated by the gaps between the rotor 3 and the poles A, B,C, and D. As the rotor 3 is of such configuration that the change inreluctance of the poles corresponds to the trigonometric function of onecycle in each rotation of the rotor 3 as earlier mentioned, thepermeances P_(A) to P_(D) are each expressed by Equations (1) set outbelow. In other words, the rotor 3 is so formed and disposed as toproduce such changes in permeance as expressed by Equations (1) inresponse to the rotation angle θ and such requirement can be met withease by an eccentrically disposed rotor as described above.

    P.sub.A =P.sub.0 +P.sub.1 sin θ

    P.sub.B =P.sub.0 -P.sub.1 cos θ

    P.sub.C =P.sub.0 -P.sub.1 sin θ

    P.sub.D =P.sub.0 +P.sub.1 cos θ                      (1)

P₀ and P₁ are constants determined in accordance with the size andpermeability, etc. of the rotor 3. In Equations (1), the rotation angleθ is 0° when the gap between the rotor 3 and the pole D is at a minimumas shown in FIG. 1(b). The figures φ_(A), φ_(B), φ_(C), and φ_(D)indicate the values of flux passing through the gaps between the rotor 3and the poles A, B, C, and D, respectively. As obvious from theequivalent circuit, they are in such relation to one another as:

    φ.sub.A +φ.sub.B +φ.sub.C +φ.sub.D =0      (2)

Magnetic potential U of the entire equivalent circuit is expressed as,

    U=Nia+φ.sub.A /P.sub.A =Nib+φ.sub.B /P.sub.B

    =-Nia+φ.sub.C /P.sub.C =-Nib+φ.sub.D /P.sub.D      (3)

The flux values φ_(A) to φ_(D) can therefore be expressed as,

    φ.sub.A =(U-Nia)P.sub.A

    φ.sub.B =(U-Nib)P.sub.B

    φ.sub.C =(U+Nia)P.sub.C

    φ.sub.D =(U+Nib)P.sub.D                                (4)

The voltages e_(A), e_(B), e_(C), and e_(D) induced by the secondarycoils 7A, 7B, 7C and 7D in accordance with the gaps between the rotor 3and the poles A to D are expressed, with N₂ indicating the number ofturns of the secondary coils 7A to 7D, as,

    e.sub.A =N.sub.2 d/dt φ.sub.A

    e.sub.B =-N.sub.2 d/dt φ.sub.B

    e.sub.C =N.sub.2 d/dt φ.sub.C

    e.sub.D =-N.sub.2 d/dt φ.sub.D                         (5)

The synthesized output signal E by the secondary coil 7 (7A to 7D) maybe expressed using Equations (5), (4), (3), (1) as well as i_(a) =I sinωt and i_(b) =I cos ωt as follows: ##EQU1## Here, it is known fromEquations (1) that P_(A) -P_(B) +P_(C) -P_(D) =0. Substituting K for thecoefficient 2N₂ NP₁ I which is constant, the following equation

    E=K sin (ωt-θ)                                 (7)

is obtained. As Equation (7) shows clearly, the output signal E isshifted in phase by the phase angle corresponding to the rotation angleθ with respect to the phase of the reference AC signal I sin ωt.

FIG. 3(a) and FIG. 3(b) show an embodiment of the invention wherein thestator 1 is of the same arrangement as in the embodiment shown in FIG. 1while a rotor 8 varies from the rotor 3 shown in FIG. 1 in that therotor 8 is cylindrical with a free end obliquely cut and is coaxiallymounted on the shaft 4. The gaps between the turning rotor 8 and theends of the poles A to D do not vary but the area with which the turningrotor 8 opposes the pole ends changes according to the rotation angle θof the rotor 8. The rotor 8 shown in FIG. 3 is thus capable, as therotor 3 shown in FIG. 1, of altering the reluctance caused by the gapsbetween the rotor 8 and the poles A to D according to the rotation angleθ. In other words, the permeance can be altered in the same manner asshown in Equations (1).

FIGS. 4(a), 4(b) and FIGS. 5(a), 5(b) show embodiments with stators 9and 9' which are modifications of the stator 1 shown in FIG. 1 and FIG.3. The stator 9 shown in FIG. 4 has four poles 9A, 9B, 9C and 9Ddisposed with an interval of 90° relative to each adjacent pole in acircumferential direction and an output pole 9E disposed on the lineextended from the shaft 4. Similarly to the embodiment shown in FIG. 1,the pole pair 9A and 9C has the primary coils 2A and 2C wound thereonand is excited by a sine wave signal i_(a) =I sin ωt while the otherpole pair 9B and 9D has the primary coils 2B and 2D wound thereon and isexcited by a cosine wave signal i_(b) =I cos ωt. On the output pole 9Eis wound the primary coil 7 which by itself is capable of collecting thecomposite signal E of the induced voltages by the poles 9A to 9D. Whilein the embodiments shown in FIG. 1 and FIG. 3, the poles A to D aredisposed in radial directions, the poles 9A to 9E are disposed in axialdirections in the embodiments shown in FIG. 4 and FIG. 5. Referring toFIG. 4, a rotor 10 is a disk eccentrically mounted on the shaft 4. Thedistance between the rotor 10 and the ends of the poles 9A to 9D remainsconstant while the rotor 10 rotates but the area with which the rotor 10opposes each pole varies according to the rotation angle θ so that thepermeance can be altered in the same manner as shown by Equations (1).

The stator 9' shown in FIG. 5 is of the same structure as the stator 9shown in FIG. 4 except for the output pole 9E' which is a little longerthan the other poles 9A to 9D. The rotor 11 is a cylinder with anoblique free end so that the gaps between the rotor 11 and the poles 9Ato 9D change according to the rotation angle θ. Permeance can thereforebe altered in this embodiment in the same way as indicated by Equations(1).

The AC signals to excite the pole pairs A and C (9A and 9C) as well as Band D (9B and 9D) are not limited to sine and cosine wave signals butmay be a combination of a sine wave signals and an inverted signal of acosine wave signal (-cos ωt) or a combination of a cosine wave signaland an inverted signal of a sine wave signal (-sin ωt) provided that oneAC signal is 90° out of phase with the other.

FIGS. 6 through 13 show embodiment for obtaining data on the rotationangle of the rotor based on the output of the detection head unitsillustrated in FIGS. 1, 3, 4 and 5.

Referring to FIG. 6, a detection head unit 12 has the stator 1 (9, 9')and the rotor 3 (8, 10, 11) shown in FIG. 1, 3, 4 or 5. With regard tothe detection head unit 12, the primary coils 2A, 2C and 2B, 2D as wellas the secondary coil 7 are schematically shown but illustration of theother parts are omitted. The embodiment shown in FIG. 6 consists mainlyof a reference AC signal generation circuit 13 and a phase differencedetection circuit 14 for obtaining data on the rotation angle based onphase shift. An oscillator 15 oscillates a high-rate clock pulse CP. Afrequency division circuit 16 frequency divides said clock pulse CP by Mto output a duty 50% pulse Pb and an inverted signal Pa of said pulse Pb(M is any given integer). More specifically, the frequency divisioncircuit, comprising a 2/M frequency divider 17 and a 1/2 flip-flopcircuit 18, obtains from the 2/M frequency divider 17 a pulse Pc namely,the 2/M-frequency-divided clock pulse CP and then frequency divides thatpulse Pc by 2 through the flip-flop circuit 18. As a result, theflip-flop circuit 18 outputs a 50% duty cycle square wave pulse Pb witha one M-th the frequency of the clock pulse CP from the output (Q) andoutputs a square wave pulse Pa namely, inverted pulse Pb from theinverted output (Q). The pulses Pb and Pa, one 180° out of phase withanother, are applied to 1/2-frequency-dividing flip-flop circuits 19,and 20 respectively to halve the frequencies of the pulses Pb and Pa andobtain pulses 1/2Pb and 1/2Pa. FIG. 7 indicates the pulses CP, Pc, Pb,Pa, 1/2Pb, and 1/2Pa for comparison. It is noted that the pulses 1/2Pband 1/2Pa which are respectively outputted from the flip-flop circuits19 and 20 have a one 2M-th the frequency of the clock pulse CP and are20° out of phase with one another. The pulses 1/2Pb and 1/2Pa areapplied to low-pass filters 21 and 22 respectively to obtain fundamentalwave components. Suppose a cosine wave signal cos ωt is outputted fromthe low-pass filter 21, then a sine wave signal sin ωt is necessarilyoutputted from the low-pass filter 22. The signal cos ωt outputted fromthe low-pass filter 21 is amplified by an amplifier 23 to obtain thesignal I cos ωt which in turn is applied to the primary windings 2B and2D wound on the pole pair B and D (9B and 9D). The signal sin ωtoutputted from the low-pass filter 22 is amplified by an amplifier 24 toobtain the signal I sin ωt which in turn is applied to the primarywindings 2A and 2C wound on the other pole pair A and C (9A and 9C).

As above mentioned, from the output winding 7 is obtained the AC signalsE=K sin (ωt-θ) which is shifted in phase with respect to the signal Ksin ωt by the phase angle corresponding to the rotation angle θ. Theoutput signal E is applied through an amplifier 25 to a polaritydiscrimination circuit 26. To another polarity discrimination circuit 27is applied one of the exciting AC signals I sin ωt through the amplifier24. The polarity discrimination circuits 26 and 27, composed ofcomparators, output "1" when the amplitude of the input signal (K sin(ωt-θ), I sin ωt) is of a positive polarity and output "0" when suchamplitude is of a negative polarity.

The outputs from the polarity discrimination circuits 26 and 27 arerespectively applied to rise detection circuits 28 and 29, namely,monostable multivibrators which output one shot of short pulse when theinput signal rises to "1". Therefore, as shown in FIG. 8, when the phaseangle (ωt-θ) of the rotation angle detection signal E is 0°, the risedetection circuit 28 outputs a rise detection pulse Ts while, when thephase angle ωt of the exciting AC signal I sin ωt is 0°, the risedetection circuit 29 outputs a rise detection pulse To. The rotationangle detection signal E=K sin (ωt-θ) is behind the exciting AC signal Isin ωt by a phase angle corresponding to the rotation angle θ.Therefore, the rise detection pulse Ts follows the rise detection pulseTo at a time interval corresponding to the phase difference θ.

It is possible to obtain data corresponding to the phase differenceθ(rotation angle) by counting the time interval between the risedetection pulses To and Ts with a counter 30 to which is applied theclock pulse CP sent by the oscillator 15. The exciting AC signals I sinωt and I cos ωt have a one M-th the frequency of the clock pulse CP sothat one cycle of the clock pulse CP corresponds to the absolute phasevalue of 2π/2M=π/M (radian). A count "1" given by the counter 30,therefore, corresponds to the absolute phase value of π/M (radian). Thecounter 30 of modulo 2M should preferably be employed so as to becapable of counting the value (2π÷π/M=2M) corresponding to the largestphase difference (largest rotation angle) of 360° (2π). To the counter30 is applied as a reset input the pulse To representing phase 0 of theexciting AC signal I sin ωt. The counter 30, therefore, is reset everytime the exciting AC signal I sin ωt is in phase 0.

The output of the counter 30 is applied to a buffer register 31 to whichis given as a sampling clock input a pulse Ts representing phase ωt-θ=0of the rotation angle detection signal K sin (ωt-θ). A count given bythe counter 31 is transmitted to the buffer register 31 at everygeneration of the pulse Ts so that the buffer register 31 receives acount corresponding to the phase difference, namely, rotation angle θ.Said count given to the buffer register 31 is the absolute value dataD.sub.θ indicating the rotation angle θ. That is, as earlier mentioned,since a count "1" corresponds to the absolute phase value of π/M(radian), the count data D.sub.θ corresponding to the rotation angleθ(radian) is the absolute value data θ/πM.

It is thus possible to compose an absolute rotary encoder by using asignal identical to the clock pulse CP which determines the frequency ofthe exciting AC signal for calculating the phase difference θ.Furthermore, it is possible to determine resolution of the encoder asdesired by freely fixing the value of M. Specific arrangements of thecircuits 13 and 14 are not limited to those shown in FIG. 6 but may befreely modified. For the counter 30 may be used not only a binarycounter but a binary-coded decimal counter as well as other counters ofsuitable code forms. By freely selecting the form of counter to be used,absolute rotation angle data D.sub.θ is available in a desired data form(binary, binary-coded decimal, or the like). Also, if a counter and abuffer register each of edge trigger type are used for the counter 30and a register 31 respectively, it is possible, without the risedetection circuits 28 or 29, to trigger the counter by the rise of theoutput pulses of the circuits 26 and 27.

FIG. 9 shows an example wherein the 2/M frequency divider 17 shown inFIG. 6 is omitted while the counter 30 of modulo 2M is shared by areference AC signal generation circuit 13A and the phase differencedetection circuit 14. In FIG. 9, the same reference figures as used inFIG. 6 designate circuits performing like functions. The bit with a onefourth the weight of the most significant bit, namely, an input at 2/Mfrequency division stage is applied to the flip-flop circuit 18 as pulsePc. Based on that pulse Pc, the sine wave signal I sin ωt and cosinewave signal I cos ωt are generated through the circuits 18 to 24 as inthe example shown in FIG. 6. The output signal E=K sin (ωt-θ) of thedetection head unit 12 is processed by the circuits 25, 26 and 28 as inthe case shown in FIG. 6 and as a result, the pulse Ts corresponding tosaid output signal E in phase 0 is given to the sampling control inputof the register 31. To the data input of the register 31 is given thecount output of the counter 30. The digital data D.sub.θ correspondingto the phase difference θ are thus memorized by the register 31 as inthe example shown in FIG. 6.

While the angle data D.sub.θ is obtained in digital by the phasedifference detection circuits 14, 14A shown in FIGS. 6 and 9respectively, they may be obtained in analog as shown in FIGS. 10 and12.

In FIG. 10, to a phase difference detection circuit 14B are applied thereference AC signal I sin ωt and the output signal E of the detectionhead unit. Supposing the output signal E has a wave form as shown inFIG. 11(a), a polarity discrimination circuit 36 outputs "1" in responseto a positive polarity and "0" in response to a negative polarity asshown in FIG. 11(b). A rise detection circuit 37 outputs short pulses asshown in FIG. 11(c) in response to the rise timing of the output (b) ofthe polarity discrimination circuit 36. The reference AC signal I sin ωtis rectified through the polarity discrimination circuit 38 as shown inFIGS. 11(d), (e) and then applied to the 1/2 frequency division circuit39 from which is obtained the output(f) that repeats "1" and "0" forevery one cycle of the reference AC signal I sin ωt. The output (f) ofthe 1/2 frequency division circuit 39 is given to an integration circuit40 to obtain an analog voltage signal (g) corresponding to the length oftime elapsed as from the rise point or fall point of the frequencydivision circuit output (f) as shown in FIG. 11(g). The output (g) ofthe integration circuit 40 is applied to a sample and hold circuit 41 tobe sampled at a timing of the phase angle of the signal E (FIG.8(a))=0°. To the sampling control input of the sample and hold circuit41 is given an output (c) of the rise detection circuit 37 through agate 42 which is enabled to allow the sample and hold circuit 41 toreceive the output pulse C of the rise detection circuit 37 when theoutput (f) of the 1/2 frequency division circuit 39 is "1" but inhibitsthe pulse (c) when the output (f) is "0". The gate 42 is provided toinhibit the sampling of the negatively inclined output (g) which theintegration circuit 40 gives when the output (f) of the 1/2 frequencydivision circuit 39 is "0" as shown in FIG. 11(g). Consequently, asampling pulse (h) is sent to the circuit 41 through the gate 42 whenthe output (g) of the integration circuit 40 is of a positiveinclination as shown in FIG. 11(h). The sample and hold circuit 41 thuscarries out sampling every other cycle to output analog DC voltage V₇₄corresponding to the phase difference θ(machine position to be detected)between the reference AC signal I sin ωt and the detection head outputsignal E.

FIG. 12 shows another example of the phase difference detection circuit14C which detects the phase difference θ in analog and which comprises apolarity discrimination circuit 43 to which the reference signal I sinωt is applied, 1/2 frequency divider circuit 44 and integration circuit45 respectively operating in the same manner as the circuits 38, 39 and40 shown in FIG. 10. The output signal E of the detection head unit isgiven to the polarity discrimination circuit 46 of which the output istransmitted to a D flip-flop circuit 47 as well as to an AND gate 48. ToD input of the D flip-flop circuit 47 is given the output of the 1/2frequency division circuit 44. The output signal of the flip-flopcircuit 47 is given to the sampling control input of a sample and holdcircuit 50 while being inverted by an inverter 49 to be added to the ANDcircuit 48. The output voltage of the integration circuit 45 is appliedto the data input of the sample and hold circuit 50 of which the outputis given to the data input of a sample and hold circuit 51. To thesampling control input of the circuit 51 is applied the output of theAND circuit 48.

Referring to FIG. 12, suppose the reference AC signal I sin ωt and thedetection head unit output signal E have wave form as shown in FIG.13(a), the outputs (b) to (h) of the circuit 43, 44, 46, 47, 45, 50 and48, respectively, have wave form each as shown in FIG. 13(b) through(h). As is obvious from FIG. 13, finally held by a circuit 51 is theintegration circuit output voltage which corresponds to the detectionhead output signal E in phase ωt-θ=180°. Because the integration circuit45 is adapted to perform its integration operation when the reference ACsignal I sin ωt is in phase ωt=180°, finally held by the circuit 51 isanalog voltage V.sub.θ corresponding to the phase shift θ. The circuit14C comprises a positive peak hold circuit 52 and negative peak holdcircuit 53 which hold the positive peak voltage +MAX and negative peakvoltage -MAX, respectively, of the output voltage of the integrationcircuit 45. The output voltages MAX and -MAX of the circuits 52 and 53can be used as reference voltages for calculating the angle θ from themagnitude of the angle detection voltage signal V.sub.θ, for thenegative peak voltage -MAX corresponds to the phase θ=0° and thepositive peak voltage MAX corresponds to the phase θ=360°.

According to the invention, one pole pair may be disposed on aconcentric but different circumference from another, instead of on thesame circumference, as illustrated in FIG. 14(a) and (b). The statorconsists of a stator 1A and stator 1B, one axially disposed with respectto another. The stator 1A has poles A and C radially opposite to oneanother with primary coils 2A and 2C on the respective poles connectedin series so that the flux in one pole and the flux in the other mayflow in opposite direction. The poles A and C are excited by a sine wavesignal I sin ωt. The stator B likewise has radially opposite poles B andD on which are wound primary coils 2B and 2D connected in series so thatthe flux in one pole and the flux in the other may flow in oppositedirections. The poles B and D are excited by a cosine wave signal I cosωt. The stators 1A and 1B are disposed with respect to one another insuch a manner that one pole pair A and C is at right angles to anotherpole pair B and D. The outputs of the secondary coils 7A to 7D arecollected as a whole as in the case shown in FIG. 1. A rotor 32 isformed of a cylindrical core and eccentrically mounted on the shaft 4similarly to the rotor 3 shown in FIG. 1.

FIG. 15(a) illustrates another modification of the embodiment accordingto the invention comprising an E-shaped stator 33 which has on itsopposite ends poles 33A and 33B with primary coils 34A and 34B woundthereon, respectively. The poles 33A and 33B are each excited by a sinewave signal I sin ωt and cosine wave signal I cos ωt. Intermediatelylocated on the stator 33 is a pole 33E with a secondary coil 7 woundthereon. A rotor 35 is formed of a cylindrical core with both endsobliquely cut and coaxially mounted on the shaft 4. Both ends of therotor 35 are not parallel to each other but one oblique end plane is 90°twisted with respect to the other. As the area with which the peripheralsurface of the rotor 35 opposes the ends of the poles 33A and 33B variesaccording to the rotation angle θ of the rotor 35, it is possible toobtain the change in reluctance corresponding to the rotation angle θ.Said 90° twisted relation between both ends of the rotor 35 results inthe change in reluctance of the pole 33A being 90° out of phase withthat of the pole 33B. The same effect can be thus obtained as in thecase where the pole 33A excited by a sine wave signal is disposed 90°out of phase with the pole 33B excited by a cosine wave signal. Morespecifically, it is possible to obtain, from the secondary coil 7 on thepole 33E, the AC signal which is shifted in phase according to therotation angle θ of the rotor 35 as in the case of the embodiments shownin FIGS. 1, 3, 4 and 5. It is also feasible according to the inventionas shown by a chain line in FIG. 15, to provide a like E-shaped stator33' so as to oppose the stator 33 with the rotor 35 therebetween, whilewinding on the poles 33A and 33C in a differential manner primary coils33A and 33C excited by a sine wave signal and likewise winding on thepoles 33B and 33D in a differential manner primary coils excited by acosine wave signal. In that case, a sum of outputs of the secondarycoils on the intermediate poles 33E and 33E' provided on the respectivestators 33 and 33' is the AC signal K sin (ωt-θ) shifted in phaseaccording to the rotation angle θ.

Reverting to Equation (7), the phase difference θ does not vary withtime, meaning that the shaft 4 is at a standstill with a given rotationangle θ. When, therefore, the shaft 4 is rotating at a given angularvelocity or angular acceleration, the phase difference θ (rotationangle) in Equation (7) is given as a function of time (t) as,

    E=K sin {ωt±θ(t)}                           (8)

The signs (±) for the phase difference function θ(t) indicate thedirection of the phase difference (phase advance or phase lag) andcorrespond to the direction of rotation of the shaft 4. Description willnow be given with this direction of phase difference limited to thedirection of phase advance, i.e. +θ(t), for simplicity. The phasedifference function θ(t) contains the element of the angular velocity orangular acceleration of the shaft 4.

When the shaft 4 is rotating at an angular velocity ω_(M),

    d/dt θ(t)=ω.sub.M                              (9)

is established and, as the integral of the angular velocity ω_(M)corresponds to the phase difference θ(t), Equation (8) can be rewrittenas,

    E=K sin {(ω+ω.sub.M)t+θ.sub.0 }          (10)

wherein θ₀ indicates the initial phase.

When, on the other hand, the shaft 4 is rotating at an angularacceleration α_(M),

    d/dt θ(t)=α.sub.M t                            (11)

hence,

    θ(t)=∫α.sub.M tdt=αM/2 t.sup.2 +θ.sub.0 (12)

Equation (8), therefore, can be rewritten as,

    E=K sin {(ω+αM/2 t)t+θ.sub.0 }           (13)

As obvious from Equation (10) or (13), the phase difference of therotation angle detection signal E which is outputted from the detectionhead unit 12 contains the element of the rotation angular velocity ω_(M)or rotation angular acceleration α_(M) so that the rotation speed orrotation acceleration can be found by analyzing the phase shift θ(moregenerally, θ(t)). It is therefore possible according to the invention todetect not only the rotation angle but the rotation speed as well asrotation acceleration. The buffer register 31 shown in FIG. 6 or 9samples the rotation angle data D₇₄ for every one cycle of the rotationangle detection signal E. When the shaft 4 is at a standstill with agiven rotation angle θ, the rotation angle data D.sub.θ retains aconstant value corresponding to the rotation angle θ. When the shaft 4is rotating at a velocity ω_(M) or acceleration α_(M), the rotationangle data D.sub.θ varies at every sampling timing. It is thereforepossible to find the angular velocity ω_(M) or angular accelerationα_(M) based on the change of the rotation angle data D.sub.θ.

Description will now be given as to how to more specifically find theangular velocity ω_(M) or angular acceleration α_(M). Shown in FIG. 16by a chain line is an example of a rotation angle detection signal Es,namely, the rotation angle detection signal E obtained when the shaft 4is rotating at an angular velocity ω_(M). The solid line represents thereference AC signal I sin ωt while the broken line shows a rotationangle detection signal Eo, namely, the rotation angle detection signal Eobtained when the rotor is at a standstill with a given rotation angleθ. The initial phase of rotation of the signal Es is θ. The figure t_(o)indicates one cycle of the rotation angle detection signal Eo and isidentical to the cycle of the exciting AC signal I sin ωt on which thephase detection is based. The figure t_(s) indicates one cycle of therotation angle detection signal Es. It is noted from FIG. 16 that, whilethe shaft 4 is rotating, the frequency of the rotation angle detectionsignal E(i.e., Es) deviates from the reference frequency (ω). This isalso obvious from Equation (10) and, more specifically, the frequencydeviation corresponds to the angular velocity ω_(M). Letting the angularfrequency of the rotation angle detection signal Es be ω_(s), Es can beexpressed from Equation (10) as,

    Es=K' sin (ω.sub.s t+θ.sub.o)

    =K' sin {(ω+ω.sub.M)t+θ.sub.o }          (14)

In FIG. 16, Δθ is difference between the phase difference θ_(o), bywhich the reference signal I sin ωt is, at a given time, different inrelation to the rotation angle detection signal E (i.e., Es) on onehand, and a phase difference θ_(s) by which the reference signal I sinωt is, t_(s) seconds later, different in relation to the rotation angledetection signal E on the other. When the shaft 4 is stationary, θ_(o)=θ_(s) and Δθ=0 while the shaft 4 is rotating, Δθ corresponds to theangular velocity ω_(M) of the shaft 4. More specifically, letting theperiod t_(o) of the reference signal I sin ωt be 2π(radian) as is clearfrom FIG. 16, the phase value corresponding to the time t_(s) is##EQU2## and Δθ is expressed as, ##EQU3##

As is known from Equation (14),

    ω.sub.s =ω+ω.sub.M

    ω=ω.sub.s -ω.sub.M

(16)

Substituting these into Equation (15). ##EQU4## is obtained. Since##EQU5## As is obvious from Equation (17), Δθ is a function of theangular velocity ω_(M).

Solving Equation (17) for ω_(M),

    Δθ=ω.sub.M ·t.sub.s

    ω.sub.M =Δθ/t.sub.s                      (18)

is obtained. The angular velocity ω_(M) can be found on the basis of Δθand t_(s). Specifically, t_(s) is obtained by counting one cycle of therotation detection signal E (I.e., Es) by the clock pulse CP. Lettingthe count value corresponding to t_(s) be n_(s) and letting one cycle ofthe clock pulse CP be φ(sec.),

    t.sub.s =n.sub.s ·φ                           (19)

The value Δθ may also be obtained on the basis of said count n_(s).Letting the number of counts of the clock pulse CP corresponding to onecycle t_(o) of the reference signal I sin ωt be n_(o), the angularfrequency ω is expressed as

    ω=2π1/t.sub.o =2π1/n.sub.o ·φ     (20)

Substituting Equation (20) into Equation (15) and solving theintegration term, ##EQU6##

Substituting Equations (21) and (19) into Equation (18), ##EQU7## isobtained, where n_(o) is a constant corresponding to a frequencydivision ratio 1/2M and n_(o) =2M. The period φ of the clock pulse CP isa known constant. As is obvious from Equation (22), therefore, theangular velocity ω_(M) can be found by counting one cycle of therotation angle detection signal E to obtain the count n_(s), and thenmerely solving Equation (22). Since ω_(M) =ω_(s) -ω from Equation (16),the same solution may be alternatively obtained by solving ##EQU8##

Between the angular acceleration α_(M) and angular velocity ω_(M) can beestablished the following relation,

    α.sub.M =d/dtω.sub.M ≃ΔωM/Δt (23)

wherein Δω_(M) is the amount of change in the angular velocity ω_(M)during time change Δt. Letting the angular velocity at a time t₁ beω_(M1) and letting the angular velocity at a time t₂ which is t_(s)seconds later than t₁ be ω_(M2),

    Δt=t.sub.s, Δω.sub.M =ω.sub.M2 -ω.sub.M1

and since t_(s) =n_(s) ·φ from Equation (19), Equation (23) can berewritten as, ##EQU9##

The angular acceleration α_(M), therefore, can be calculated bydetecting the angular velocity ω_(M) for every one cycle t_(s) of therotation angle detection signal E(i.e., Es) to find the differencebetween the angular velocity ω_(M2) and the angular velocity ω_(M1), anddividing that difference by the product of the count n_(s) and theperiod φ of the clock pulse CP.

Description will now be made, with reference to FIGS. 17 through 23, ofan example of a circuit whereby to obtain velocities and accelerationsby performing the above operations.

In FIG. 17, circuits 15 through 24 provided to supply the primary coils2A, 2C, 2B and 2D of the detection head unit 12 with the sine wavesignal I sin ω_(t) and cosine wave signal I cos ω_(t) are each identicalto the circuits with the same reference numerals forming the circuit 13shown in FIG. 6 except that in FIG. 17, the output signals 1/2Pa and1/2Pa' of the output terminal Q and its inverted output terminal Q ofthe flip-flop circuit 20 are applied to a circuit 54 which selects andapplies one of said output signals to the low-pass filter 22 so that, aswill be described later, the exciting signals may be switched over inphase by 180° according to the direction of rotation.

As earlier mentioned, from the secondary coil 7 of the detection headunit is obtained the AC signal E=ES=K' sin (ω_(s) t+θ_(o)) deviated infrequency by ω_(M) corresponding to the rotation speed. While thedirection of the frequency deviation ω_(M) with respect to the referencefrequency ω depends on the rotational direction of the shaft 4,description will now be made on the supposition that the shaft 4 isrotating in a positive direction, namely in such a direction that thefrequency ω_(s) is higher than the reference frequency ω. Said positivedirection will be hereinafter referred to as clockwise direction.

The speed detection circuit 55 is provided to obtain the rotation speedbased on the output signal E(Es) of the detection head unit 12 andcomprises a period computation circuit 56, computation circuit 57 andlatch circuit 58. The period computation circuit 56 is provided toobtain the period t_(s) of the output signal E(Es) of the detection headunit 12 and outputs the count n_(s) corresponding to t_(s) by countingone cycle of the signal Es against the clock pulse CP. The output signalE(Es) is inputted to a comparator 59 which outputs "1" or "0" dependingon the polarity of the input signal E. A monostable multivibrator 60outputs one shot of pulse G (lasting, for example, for the period ofabout 100 nano seconds) at the rise of the output signal F. A monostablemultivibrator 61 outputs one shot of pulse H at the fall of the pulse G(see FIG. 18). The pulse G, therefore, is generated keeping pace withthe period t_(s) of the output signal E(Es) while the pulse H isproduced a little behind the pulse G. A frequency division circuit 62frequency divides the clock pulse CP by 2 and a counter 63 counts theoutput of the circuit 62. To the reset input of the counter 63 issupplied the pulse H. The count output of the counter 63 is applied to aregister 64. To the load control input of the register 64 is suppliedthe pulse G. Therefore, the counter 63 is reset immediately after acount is loaded to the register 64 by the pulse G. Because the counter63 is reset by the pulse H every one cycle t_(s) of the output E(Es),the counter 63 retains the count n_(s) corresponding to t_(s) at atiming of the pulse G immediately before the pulse H. Said value n_(s)is memorized by the register 64.

The computation circuit 57 performs the operation of Equation (22). As2π, n_(o), φ are known constants, the operation can be performed, withthe count n_(s) memorized by the register 64, in the following order:

    n.sub.0 -n.sub.s . . . R.sub.1                             ○ 1

    R.sub.1 /n.sub.s . . . R.sub.2                             ○ 2

    2π/(n.sub.o ·φ)×R.sub.2 . . . R.sub.3 ○ 3

wherein R₁, R₂ and R₃ are the results of the above respective steps ofcalculations. Since in this example, the counter 63 countsfrequency-halved clock pulse CP, the figure φ in the above formulaindicates double the period of the clock pulse CP. In other words, theclock pulse CP has a period φ/2 in this example. The other constants arespecified as follows. The period to of the reference CA signal I sin ωt,which is obtained by frequency dividing the clock pulse CP by 2M, is φMnamely 2M times the cycle of the clock pulse CP. The count n_(o)corresponding to the period t_(o) is calculated by n_(o) =t_(o) /φ=M. Ifthe frequency division factor M of the frequency division circuit 16 is9766, then n_(o) =9766. If the frequency of the clock pulse CP is 3.2MH_(z), φ=1/1600000.

The number of revolutions per second (r.p.m.) can be obtained bydividing by two the angular velocity ω_(M) calculated by Equation (22).In general the rotation speed is expressed by the number of revolutionsrather than by the angular velocity ω_(M). In the computation circuit57, therefore 1/n_(o) ·φ obtained by dividing the coefficient by 2π maypreferably be used in the multiplication in the operational step ○3which therefore is modified as follows:

    1/(n.sub.o ·φ)×R.sub.2 . . . R.sub.3    ○ 3'

The result R₃ (ωM/2π) thus obtained, which indicates the rotation speedof the shaft 4, is latched by the latch circuit 58. Data is loaded tothe latch circuit 58 at a timing of the pulse G so that data X,indicating the rotation speed and retained in the latch circuit 58, isrewritten every cycle t_(s) of the output signal E. The computationcircuit 57 has the clock pulse CP and pulse G applied thereto to controlthe operation timing. The calculation step ○3 may of course be performedas such to obtain the angular velocity ω_(M).

A digital comparator 65 is provided to detect the rotational directionof the shaft 4 by comparing the count n_(s) outputted from the register64 with the reference count n_(o). The comparator 65 outputs "1" at atiming of the pulse G when n_(s) >n_(o) and "0" in other cases. Theoutput of the comparator 65 is applied to the switch-over circuit 54which switches the pulse it selects from the pulse 1/2Pa to 1/2Pa' orvice versa every time "1" is given from the comparator 65.

Suppose the switch-over circuit 54 is now selecting the pulse 1/2Pa andthe rotational direction is clockwise while the frequency ω_(s) of theoutput E(Es) is higher than the reference frequency (ω_(s) >ω). Thenn_(s) <n_(o) and the comparator 65 outputs "0" so that the circuit 54 isstill selecting the pulse 1/2Pa. When, in this state, the rotationaldirection changes to become counterclockwise, the angular velocity ω_(M)assumes a negative value -ω_(M) and ω_(s) <ω while n_(s) >n_(o). Theoutput of the comparator, therefore, changes to "1" with the result thatthe pulse selected by the switch-over circuit 54 is switched from thepulse 1/4Pa to pulse 1/4Pa' meaning that i_(a) in Equation (6) changesto -1 sin ωt as the output of the filter 22 corresponding to the pulse1/2Pa' is -sin ωt. Substitution of -I sin ωt for i_(a) in Equation (6)will show that the polarity of the output signal E is only reversedwhile, on the other hand, the direction of the phase shift θ remains thesame as a result of change in the rotational direction of the shaft 4.In other words, while change in the rotational direction results ininversion of the direction of the phase difference θ of the outputsignal E from positive to negative or vice versa in case the directionof the phase difference of the primary-windings-exciting signals i_(a)·i_(b) remain the same, it is possible to keep the phase difference θ ofthe output signal E in the same direction at all times by reversing thephase of the primary-winding-exciting signals i_(a), i_(b) when therotational direction is inversed. The relation n_(s) <n_(o) is thusestablished with respect to the counterclockwise rotation by switchingthe exciting signals and the output of the comparator 65, therefore,changes to "0" immediately. Upon inversion of the rotational directionfrom counterclockwise to clockwise while the pulse 1/2Pa' is beingselected by the switch-over circuit 54, the relation n_(s) >n_(o) isestablished and the comparator 65 outputs "1" as mentioned above withthe result that the switch-over circuit 54 is switched to select thepulse 1/2Pa. Therefore, the relation n_(s) <n_(o) is immediately set upfor the clockwise rotation.

The comparator 65 and switch-over circuit 54 thus serve to realize therelation n_(s) <n_(o). As a result, the computation circuit 57 can besimple in composition (because n_(o) -n_(s) is always positive).Moreover, the rotation speed data X outputted from the latch circuit 58can be processed easily because such an extra circuit is dispensed withas is required to obtain the absolute value of the rotation speed data Xwhich is outputted from the latch circuit 58 either as a positive ornegative value depending on the rotational direction where thecomparator 65 and switch-over circuit 54 are not provided. The presentinvention, however, may of course be worked without the comparator 65and switch-over circuit 54. The acceleration computation circuit 66performs the operation of Equation (24) on the basis of the velocitydata obtained by the speed detection circuit 55 thereby to find theacceleration α_(M). To the acceleration computation circuit 66 isapplied data latched in the latch circuit 58 as data X₁ indicating thepreceding rotation speed; the result R₃ of the above calculation step ○3' outputted from the computation circuit 57 as data X₂ indicating thepresent rotation speed; and the count n_(s) corresponding to the periodt_(s) of the signal E memorized by the register 64 as data indicatingthe time elapsed between preceding detection and the present detection.On the basis of those data, ##EQU10## is calculated to find the rotationspeed. If X₂ =ωM2/2π and X₁ =ωM12π, the above formula reduces to##EQU11## providing to be a similar computation to that carried out inEquation (24) in that from Equation (24) is obtained the angularacceleration α_(M) while by calculation of Formula (25) is directlyfound the rate of change of rotation speed per second or accelerationαM/2π. If X₁, X₂ indicate the angular velocities ω_(M1), ω_(M2),respectively, the angular acceleration α_(M) is of course obtained asshown in Equation (24) in the computation circuit 66. Data indicatingthe acceleration αM/2π obtained by the computation circuit 66 is appliedto the latch circuit 67 at a timing of the pulse G. From the latchcircuit 67 is thus outputted data indicating the rotation acceleration.The data is rewritten every cycle of the output signal E.

While in the example shown in FIG. 17, the rotation speed is calculatedon the basis of the periods t_(o), t_(s) (n_(o), n_(s)), the rotationangular velocity ω_(M) may be obtained by directly measuring thefrequency ω_(s) of the output signal E(Es) as shown in FIG. 19. Thecircuitry shown in FIG. 19 comprises circuits 18 through 24 eachperforming the same function as the circuit likewise numbered in FIG.17. Those circuits produce a sine wave signal I sin ωt and a cosine wavesignal I cos ωt on the basis of oscillatory output from an oscillationcircuit 68. The output signal E(Es) of the detection head unit 12 is toa comparator 69 which, performing the same function as the comparator 59shown in FIG. 17, outputs a pulse signal F having the same frequency asthe output signal E. A frequency measurement circuit 70 measures thefrequency ω_(s) of the pulse signal F, based on which it outputs data X₂indicating the present rotation angular velocity ω_(M). That is, sinceω_(M) =ω_(s) -ω from Equation (13), ω_(M) can be computed by measuringthe frequency ω_(s) of the signal F (i.e., output signal E).

FIG. 20 shows an example of the frequency measurement circuit 70 whereina frequency/voltage converter 70A is employed to output an analogvoltage V(ω_(M)) indicating the rotation angular velocity ω_(M). Therotation speed can be obtained very easily with this example as theoutput velocity V(ω_(M)) corresponding to the input signal F is put in aproportional relation to the difference ω_(s) -ω between the inputfrequency ω_(s) and offset frequency ω, namely to the rotation speedω_(M) by presetting the offset frequency of the frequency/voltageconverter 70A at the reference frequency ω.

FIG. 21 shows another example of the frequency measurement circuit 70where a frequency counter 70B is employed to output digital dataC(ω_(M)) indicating the rotation speed. The data C(ω_(s)) indicating thecounted frequency ω_(s) and data C(ω) indicating the reference frequencyω are inputted to a subtractor 70C to obtain velocity data C(ω_(M)).

Direct measurement of frequency as illustrated in FIG. 19 isadvantageous when a detection head unit of high resolution type to bedescribed later is employed in that frequency measurement accuracy isenhanced as the frequency difference corresponding to the rotationangular velocity is greatly enlarged by a detection head unit of thattype. Data outputted from the frequency measurement circuit 70 is heldby a memory circuit 71 at a suitable timing. To the accelerationcomputation circuit 66 are applied the output of the memory circuit 71as preceding velocity data X and the output of the frequency measurementcircuit 70 as present velocity data X₂ to obtain the acceleration α_(M)on the basis of the change (X₂ -X₁).

When the velocity ω_(M) and acceleration α_(M) are to be obtained inanalog, the frequency measurement circuit 70 may be embodied by thefrequency/voltage converter 70A as shown in FIG. 20. In general,however, frequency/voltage converters have a relatively large timeconstant and as such are limited in response to change in velocity.

For improved response to change in velocity, a cycle/voltage converteras shown in FIG. 22 may be used instead. The signal F from thecomparator 69 is applied to a reference time width generation circuit 72as well as to gate signal generation circuit 73. The waveform of thesignal F is shown in FIG. 23(a). The reference time width generationcircuit 72 is triggered by the fall of the signal F and generates pulseswith a reference time width t_(o), as shown in FIG. 23(b), whichcorresponds to one cycle of the reference AC signal I sin ωt. A rampvoltage generation circuit 74 produces ramp voltage having a certainslope each pulse starting at the fall of the reference time widthgeneration pulse, as shown in FIG. 23(c). The ramp voltage is applied toa sample and hold circuit 75. The gate signal generation circuit 73outputs a sampling pulse as shown in FIG. 23(d) corresponding to thefall of the signal F. Said sampling pulse is given to the samplingcontrol input of the sample and hold circuit 75. A reset pulse generatedat the rise of the signal F is given from the gate signal generationcircuit 73 to the ramp voltage generation circuit 74 to reset the rampvoltage as shown in FIG. 23(c).

As mentioned above, the cycle of the signal F is identical to that ofthe output signal E of the detection head unit 12 (FIG. 19) and changesaccording to the turning speed. When the turning speed is 0(stationary), one cycle of the signal F is identical to the referencetime width t_(o). Since each pulse of the ramp voltage of the rampvoltage generation circuit 74 starts at the fall of the reference timewidth t_(o), DC voltage V(ω_(M)) corresponding to the rotation speedω_(M) can be obtained by sample-and-holding the ramp voltage by thesample and hold circuit 75 at the end of every cycle of the signal F. Acycle/voltage conversion circuit as mentioned above, whereby voltageV(ω_(M)) corresponding to the rotation speed is obtained every cycle, isrich in response and detects an even extremely small difference in cyclewith high resolution.

Coupling the circuitry illustrated in FIGS. 9, 10 or 12 with thecircuitry illustrated in FIG. 17 or 19 makes it possible, with only onedetection head unit 12 provided, to detect the rotation angle θ and therotation speed ω_(M) namely, number of revolutions X (r.p.s.) as well asthe rotation acceleration α_(M) namely, rate of change in revolutionnumber α_(M) /2π, all together.

Description will now be given of an example of the detection head unitaccording to the invention which is improved over the above describedexamples of the detection head unit by providing the poles of the statorand the rotor with teeth.

In the detection head unit shown in FIGS. 24(a) and 24(b), a stator 76,like the stator 1 in FIG. 1, has four poles A, B, C and D at an intervalof 90°. Primary coils 7A-7B and secondary coils 7A-7B are wound on therespective poles A, B, C and D.

The rotor 77 is of a gear wheel configuration having a plurality ofteeth provided at an equal pitch about the periphery thereof. Each ofthe teeth of the rotor 77 consists of a recess 3a and a projection 3b.Likewise, the poles A, B, C and D of the stator 76 also have, at the endportions thereof opposing the rotor 77, teeth consisting of a recess 1aand a projection 1b with a pitch properly corresponding to the pitch ofthe teeth of the rotor 77. The teeth (3a, 3b) of the rotor 77 correspondto the teeth (1a, 1b) of the poles A-D in such a manner that amechanical phase difference corresponding to 1/2 pitch is producedbetween the poles which constitute a pair (i.e., A and C, or B and D).By this arrangement, permeance between the pole A (or B) and the rotor77 and permeance between the pole C (or D) and the rotor 77 vary in adifferential manner at a cycle equivalent to 1 pitch. Besides, amechanical phase difference which is less than 1/2 pitch is producedbetween the poles of each pole pair (i.e., A and C, or B and D). Sincethe present embodiment has two pairs of the poles (A and C and B and D),the device is designed so that a mechanical phase difference of 1/4pitch which is half of 1/2 pitch is produced. Correspondence between theteeth (3a, 3b) of the rotor 77 and the teeth (1a, 1b) of the poles A-Dof the stator 76 is shown in FIG. 25. In FIG. 25, the pitch number ofthe teeth of the rotor 77 is 9 pitches per one revolution. It should,however, be noted that this is only an example.

Since the position of the teeth (1a, 1b) of the pole A of the pole pairA, C relative to the teeth (3a, 3b) of the rotor 77 is out of phase by 1pitch to the position of the teeth (1a, 1b) of the pole C relative tothe teeth (3a, 3b), of the rotor 78, permeance in the gap between theend portion (teeth portion) of the pole C and the teeth portion of therotor 77 is minimum when permeance in the gap between the end portion ofthe pole A and the teeth portion of the rotor 77 is maximum. At arotation angle shifted by 1/4 pitch from this angle, permeance of thepole A is equal to that of the pole C whereas at a rotation angleshifted by 1/3 pitch, permeance of the pole A is minimum and that of thepole C is maximum. Thus, permeance of the pole A changes in an oppositedirection (i.e., differentially) to permeance of the pole C at a rate of1 cycle per 1 pitch. The same is the case with the other pole pair B andD. Since the pole pair B, D is provided in a position shifted by 90°from the pole pair A, C change in permeance observed in the pole pair A,C takes place at a rotation angle which is shifted by 1/4 pitch from thepole pair A, C.

Permeances P_(A) ', P_(B) ', P_(C) ', and P_(D) ' between the statorpoles A, B, C, and D and the rotor 77 change with the rotation angle θas expressed by the following equations:

    P.sub.A '=P.sub.0 +P.sub.1 sin Nθ

    P.sub.B '=P.sub.0 -P.sub.1 cos Nθ

    P.sub.C '=P.sub.0 -P.sub.1 sin Nθ

    P.sub.D '=P.sub.0 +P.sub.1 cos Nθ                    (26)

In these equations, P₀ and P₁ are constants determined in the samemanner as in the equation (1). As will be apparent from comparison ofthe equation (1) with the equation (26), the change in permeances P_(A)through P_(D) occurs cyclically for each rotation of the rotor (i.e., 1cycle per 1 rotation of the rotor) in the toothless detection head asshown in FIGS. 1(a), 1(b), 3(a), 3(b), 4(a), 4(b), 5(a), 5(b), 14(a),14(b), 15(a) and 15(b) whereas change in permeance P_(A) ' through P_(D)' occurs cyclically for each 2π/N radian (i.e., 1 cycle per 2π/N radian)corresponding to 1 pitch of the rotor teeth (3a, 3b) in the tootheddetection head. Accordingly, in the toothed detection head, the phasedifference corresponding to the rotation angle θ is enlarged to N timesand realized as Nθ in the output signal E. By exciting the poles A and Cof the stator 76 shown in FIG. 24 by means of the sine wave signal I sinωt and the poles B and D by means of the cosine wave signal I cos ωt inthe same manner as in the embodiment shown in FIG. 1, the sum outputsignal E of the secondary coils 7A-7D is expressed as follows for thesame reason as in the equations (1) nand (7):

    E=K sin (ωt-Nθ)                                (27)

As circuits for detecting the phase difference Nθ in response to thisoutput signal E, the same circuits as those shown in FIGS. 6, 9, 10 and12 may effectively be employed. If, for example, the detection headshown in FIGS. 1(a) and 1(b) is employed as the detection head 12 inFIG. 6, 1 count of the counter 30 of modulo M corresponds to π/M radianwhereas if the detection head shown in FIGS. 24(a) and 24(b) isemployed, 1 count corresponds to π/NM radian resulting in increase inresolution of detection by N times. Accordingly, the high resolutiontype detection head unit shown in FIGS. 24(i a) and 24(b) is suitablefor detecting a small rotation angle with accuracy. It is also possibleto employ the high resolution type detection head unit shown in FIGS.24(a) and 24(b) as the detection head unit 12 of FIGS. 17 and 19. Inthis case, the rotation speed ωM and the rotation acceleration 2M may bedetected with a high resolution.

Despite the high resolution, the detection head unit shown in FIGS.24(a) and 24(b) can only detect a relative rotation angle within 1 pitch(i.e., 2π/N radian) of the teeth (3a, 3b). If necessary, therefore, anarrangement may be made so that a coarse absolute rotation angle may bedetected for each tooth of the rotor 77 by suitable means and anabsolute value of the rotation angle θ of the rotor 77 may be obtainedby combining this coarse absolute rotation angle for each tooth with theabove described fine relative rotation angle. FIG. 26 schematicallyshows an example of such combination. In FIG. 26, a shaft 4 which isprovided with the rotation angle θ has two detection head units 12A and12B. The detection head unit 12B consists, as shown in FIGS. 24(a) and24(b), of a stator 76 having teeth 1a, 1b and a rotor 77 having teeth3a, 3b and detects a relative rotation angle for each tooth with a highresolution. The other detection head unit 12A is provided for detectinga coarse absolute rotation angle for each tooth. The toothless rotationheads as shown in FIGS. 1(a), 1(b), 2(a)-5(b), 14(a)-15(b) may beemployed. As the circuit 13A for generating the reference AC signal Isin ωt and I cos ωt and the circuit 14A for detecting the phasedifference θ in the secondary coil output signal E in the detection headunit 12A, circuits of the same reference characters shown in FIG. 9 maybe utilized. Similarly, the circuit 14A' detecting the phase differenceNθ in the secondary coil output signal E in the high resolution typedetection head unit 12B may be constructed in the same manner as in theabove described circuit 14A. The circuit is not limited to that of FIG.9 but the one shown in FIGS, 6, 10 or 12 or a circuit of otherconstruction may be employed. A register 31 in the circuit 14A latchesdata Dθ resulting from relatively coarse detection of the absoluterotation angle. A register 31' in the circuit 14A' latches data D_(N) θresulting from high resolution detection of the relative rotation anglewithin 1 pitch of the rotor teeth. A counter 30 and a register 31 (31')Shown in FIG. 26 perform the same function as those designated by thesame reference numerals in FIG. 9. Detailed illustration of circuitportions of the circuits 13A, 14A and 14A' which will be apparent fromFIG. 9 is omitted. The circuit 13A which generates the reference ACsignals I sin ωt and I cos ωt is used commonly for the detection headunits 12A and 12B. Relation between the phase difference detection dataDθ and D_(N)θ obtained by the circuits 14A and 14A' and the rotationangle θ is shown in portions (a) and (b) in FIG. 27. As will beappreciated from FIG. 27, the absolute rotation angle can be detectedwith a high resolution by combination of phase difference detection dataVθ and V_(N)θ detected by the detection head units 12A and 12B. For thedetection head unit 12A, a device capable of producing detection dataD.sub.θ, as shown in portion (c) of FIG. 27 which has stepped portionscorresponding to positions of the respective teeth may be employed. Thisdevice may be constructed, for example, of combination of switches,sensors and a processing circuit.

The configurations of the stator 76 and the rotor 77 are not limited tothose shown in FIGS. 24(a) and 24(b) but modification can be made withinthe scope of the invention. For example, the direction of flux passingthrough the gap between the stator 76 and the rotor 77 which is radialin FIGS. 24(a) and 24(b) may be changed to the axial direction of theshaft as shown in FIG. 28. In FIG. 28, a rotor 78 is formed with teethwith a certain pitch as in the rotor 77 shown in FIG. 24(a). A stator 79has four poles A, B, C and D projecting in the axial direction and beingprovided at an equal interval on the periphery. The end portion of eachpole has teeth opposing the teeth of the rotor 78. The poles A-D haveprimary coils 2A-2D wound thereon. An axially projecting pole 80 is alsoprovided in the central portion of the stator 79 on which pole 80 iswound a secondary coil 7.

In the embodiment shown in FIG. 24(a), the poles A-D of the stator 79are provided on the same circumference. Alternatively, the poles A and Cmay be provided in an axially displaced posision relative to the poles Band D as shown in FIGS. 29(a) and 29(b) while the same angular positionas in FIG. 24(a) is maintained. This design enables elongation of therotor 76. In FIG. 29(a), the rotor 81 is somewhat longer in the axiallength than the rotor 77 shown in FIG. 1. A stator 82 has only a pair ofpoles A and C changing in a differential manner and a stator 83 has alsoonly a pair of poles B and D changing in a differential manner. Thesestators 82 and 83 are disposed on the same shaft in such a manner thatthe pole pairs A, C and B, D are spaced from each other by 90° in thecircumferential direction. Each of the poles A, B, C and D has, as inthe poles shown in FIG. 24(a), primary coils 2A-2D and secondary coils7A-7D wound thereon.

Alternatively, as shown in FIGS. 30(a)-31(b), the stator and rotor maybe so designed that the relative angular position of the pole pairs A, Cand B, D is the same as that in the above described embodiments and amechanical phase difference of 1/4 pitch is produced in rotors 77A and77B corresponding to these pole pairs. FIGS. 30(a) and 30(b) showstators 84 and 85 which are of an E-shaped section and are opposing toeach other in a radial direction. Each of the poles A-D has a primarycoil wound thereon and each of central poles 84C and 85C has a secondarycoil wound thereon. FIGS. 31(a) and 31(b) show circular stators 82 and83 respectively having pole pairs A, C and B, D which are in the sameangular positions. A mechanical phase difference of 1/4 pitch isproduced in the teeth of rotors 77A and 77B so that the detection headunit shown in FIGS. 31(a) and 31(b) work in the same manner as thatshown in FIGS. 29(a) and 29(b).

In mounting the detection head unit to a mechanical system in whichdetection is to be made, the origin of the mechanical system and that ofthe detection head unit must be registered accurately and this requiresa precision work. For dispensing with such precision work, a phase shiftcircuit 86 for adjusting the origin may be provided between a secondarycoil 7 and a circuit 14 (or 14A-14C) for detecting phase difference. Thephase shift circuit 86 includes a resistor R₁, a variable resistor R₂and a capacitor C₁ and produces a signal E which has been phase shiftedby suitably delaying an input signal E' in accordance with time constantof the circuit. The time constant of the circuit, i.e., amount of phaseshift, is adjusted by operating the variable resistor R₂.

The Detection head unit 12 is mounted to a shaft of the mechanicalsystem in which detection is to be made by suitable means such asscrews. If the origins of the detection head unit and the mechanicalsystem are not in perfect register with each other, phase differencecorresponding to the mounting error is produced in the output signal E'.Assuming now that the present position of the mechanical system is inthe origin and the amount of phase shift in the phase shift circuit 86is 0, the phase of the output signal E' of the detection head unit 12 isnot shifted but is directly applied to the phase difference detectioncircuit 14 with a result that output data D.sub.θ of the phasedifference detection circuit 14 assumes a value corresponding to themounting error. This data D.sub.θ is displayed by a suitable indicator(not shown) and phase shifting of a suitable amount is effected in thephase shift circuit 86 by manipulating the variable resistor R₂, wherebya signal E in which the phase difference corresponding to the mountingerror is compensated can be obtained from the phase shift circuit 86. Inthis manner, an electrical adjustment of the origin is performed by thephase shift circuit 86 and, accordingly, an accurate phase shiftdetection (i.e., detection of the angle) can be made on the basis of theposition detection signal E which has been adjusted in the origin.Consequently, a high degree of precision in mounting the detection headunit to the mechanical system is not required, thus facilitating themounting work.

In the above described embodiments, the number of the pole pairs of thestator is not limited to two pairs of A, C and B, D but may be suitablyincreased. The two poles A and C (or B and D) which constitutes a pairare opposed to each other in a radial direction (i.e., at an interval of180°) but the relative position of these poles is not limited to this.The primary coils 2A-2D and the secondary coils 7A-7D need not beconnected in series but may be wound such that AC signals areindividually applied to the respective coils of the primary coils andoutputs are obtained individually from the secondary coils andthereafter are added together or subtracted from each other. In the highresolution type detection head, the recesses 1a, 3a of the teeth neednot be a vacant space but a proper non-magnetic material may be filledin these recesses.

What is claimed is:
 1. A rotation speed detection devicecomprising:stator means having a plurality of poles which include endportions, said poles being arranged in a predetermined arrangement, saidstator means further having primary coils being wound on the respectivepoles and secondary coils being wound on the respective poles inassociation with the respective primary coils; rotor means of suchconfiguration as to oppose the end portions of the respective poles withgaps therebetween, change reluctance of magnetic paths passing therespective poles in accordance with a rotational angle and receive arotational movement or displacement by rotation, which is an object ofdetection from outside; a first circuit for exciting each of saidprimary coils with one of a plurality of reference AC signals, each poleexcitation signal being out of phase with the excitation signals ofadjacent poles by a predetermined electrical angle; a second circuit forsumming outputs of the respective secondary coils and thereby generatingan output signal resulting by phase modulating the reference AC signalsin accordance with the rotation speed of said rotor means; a thirdcircuit for detecting the rotation speed of said rotor means inaccordance with the difference in frequency or period between thereference AC signals and the output signal from the second circuit; amemory circuit for temporarily storing the rotation speed data havingbeen detected by said third circuit, and a fourth circuit for detectingrotation acceleration of said rotor means in accordance with thedifference between the rotation speed data temporarily held in saidmemory circuit and rotation speed data which has been newly detected bysaid third circuit.
 2. A rotation speed detection device as defined inclaim 1 wherein said third circuit comprises a circuit for detecting aperiod of the output signal from the second circuit and a computationcircuit for effecting a predetermined computation to obtain the rotationspeed data in accordance with the detected period data and referenceperiod data corresponding to the reference AC signals.
 3. A rotationspeed detection device as defined in claim 1 wherein said third circuitcomprises a circuit for producing a square wave signal synchronized withone period of the output signal from the second circuit and aperiod-voltage conversion circuit for generating an analog voltagecorresponding to the difference between one period of the square wavesignal and one period of the reference AC signals.
 4. A rotation speeddetection device comprising:stator means having a plurality of primarypoles arranged in a predetermined arrangement, a secondary pole, primarycoils being wound on respective primary poles and a secondary coil beingwound on the secondary pole, said poles having end portions; rotor meansof such configuration as to oppose the end portions of the respectiveprimary poles and the secondary pole with gaps therebetween, changereluctance of magnetic paths passing the respective primary poles inaccordance with a rotation angle and receive a rotational movement ordisplacement by rotation which is an object of detection from outside; afirst circuit for exciting each of said primary coils with one of aplurality of reference AC signals, each pole excitation signal being outof phase with the excitation signal of adjacent poles by a predeterminedelectrical angle and thereby producing in the secondary coil an outputsignal resulting by phase modulating the reference AC signals inaccordance with the rotation speed of said rotor means; a second circuitfor detecting the rotation speed of said rotor means in accordance withthe difference in frequency or period between the reference AC signalsand the output signal of the secondary coil; and a memory circuit fortemporarily storing the rotation speed data having been detected by saidsecond circuit, and a third circuit for detecting rotation accelerationof said rotor means in accordance with the difference between therotation speed data temporarily held in said memory circuit and rotationspeed data which has been newly detected by said second circuit.
 5. Arotation speed detection device comprising:stator means having aplurality of poles which include end portions, said poles being arrangedin a predetermined arrangement, said stator means further having primarycoils being wound on respective poles and secondary coils being wound onthe respective poles in association with the respective primary coils;rotor means of such configuration as to oppose the end portions of therespective poles with gaps therebetween, change reluctance of magneticpaths passing the respective poles in accordance with a rotation angleand receive a rotational movement or displacement by rotation, which isan object of detection from outside; a first circuit for exciting eachof said primary coils with one of a plurality of reference AC signals,each pole excitation signal being out of phase with adjacent poles by apredetermined electrical angle; a second circuit for summing outputs ofthe respective secondary coils and thereby generating an output signalresulting by phase shifting the reference AC signals in accordance witha present rotation angle of said rotor means; a third circuit fordigitally detecting the phase difference between a predetermined one ofthe reference AC signals and the output signal from the second circuitto obtain detected digital phase difference data as absolute rotationangle data; a fourth circuit for detecting the rotation speed of saidrotor means on the basis of the change of said detected absoluterotation angle data; a memory circuit for temporarily storing therotation speed data having been detected by said fourth circuit; and afifth circuit for detecting rotation acceleration of said rotor means inaccordance with the difference between the rotation speed datatemporarily held in said memory circuit and rotation speed data whichhas been newly detected by said fourth circuit.